Bug 852489. Part 1: Don't create nsDisplayButtonForegrounds for buttons that aren't focused. r=mats

--HG--
extra : rebase_source : 93ad60be2d64345fee5bbdd4553b11b5d8341d18

layout/forms/nsButtonFrameRenderer.cpp

@@ -185,11 +185,18 @@ nsButtonFrameRenderer::DisplayButton(nsDisplayListBuilder* aBuilder,
       nsDisplayButtonBoxShadowOuter(aBuilder, this));
   }
 
+  // Almost all buttons draw some kind of background so there's not much
+  // point in checking whether we should create this item.
   aBackground->AppendNewToTop(new (aBuilder)
     nsDisplayButtonBorderBackground(aBuilder, this));
 
-  aForeground->AppendNewToTop(new (aBuilder)
-    nsDisplayButtonForeground(aBuilder, this));
+  // Only display focus rings if we actually have them. Since at most one
+  // button would normally display a focus ring, most buttons won't have them.
+  if ((mOuterFocusStyle && mOuterFocusStyle->StyleBorder()->HasBorder()) ||
+      (mInnerFocusStyle && mInnerFocusStyle->StyleBorder()->HasBorder())) {
+    aForeground->AppendNewToTop(new (aBuilder)
+      nsDisplayButtonForeground(aBuilder, this));
+  }
   return NS_OK;
 }